176 RECORDS. 



The following program was presented : 



A. W. Grabau, The Geology of Becraft Mountain, New 

 York. 



C. W. Dickson, The Mineralogy and Geology of the 

 Sudbury-Ontario- Copper-Nickel Deposits. 



Summary of Papers. 



Dr. Grabau said that Becraft Mountain, in Columbia Co., 

 N. Y., is an outlier of the Helderberg Mountains. Its base 

 is formed by the upturned and eroded rocks of the Hud- 

 son Group, chiefly, the Normans Kill shales. Uncomformably 

 upon this rests the upper part of the Manlius limestone, fol- 

 lowed in turn by the members of the New York Devonian up 

 to and including the Onondaga limestone. The structure of 

 the eastern and southen portion of the mountain, which is of 

 the Appalachian type was discussed, and the excessive folding 

 and faulting upon it were illustrated by maps and sections. 

 The paper was discussed by Dr. Stevenson and Dr. Julien. 



In Mr. Dickson's paper it was shown that by magnetic con- 

 centration of the ore nearly all the nickel can be eliminated from 

 the pyrrhotite, proving that the element is present in a separate 

 mineral and that it does not replace part of the iron of the pyr- 

 rhotite isomorphously. The economic concentration of the 

 nickel by magnetic methods is, however, practically impossible. 

 The composition of the nickel mineral corresponds closely to 

 that of pentlandite, but there is always an excess of (FeNi) 

 over that required by the formula (FeNi)S in the proportion 

 1 1 : lo. 



After studying the relations of the ore and rock minerals in 

 the field and by the aid of the microscope, the conclusion was 

 reached that, in their present form, the deposits are replacements 

 along crushed zones through which the mineral-bearing waters 

 circulated, and that they cannot be original magmatic segrega- 

 tions, as generally held. 



George I. Finlay, 



Sectrctary, pro tern. 



